Electrical resistor and resistance elements therefor



July 4, 1953 F. E. KERRIDGE ETAL 2,645,701

ELECTRICAL RESISTOR AND RESISTANCE ELEMENTS THEREFOR Filed May 10. 1951 [n Venlbrs fkA/VK. E. AEkR/DGE M/Cf/AEL BEN/AM GRAHAM PEARCE.

Adv/hey:

Patented July '14, 1953 ELECTRICAL RESISTOR AND RESISTANCE ELEMENTS THEREFOR Frank Enoch Kerridge and Michael Belham, London, andGraham Pearce, Kingsthorpe, North- 'ampton,- England,

assignors to Johnson,

Matthey & Company Limited, London, England, and Painton & Company Limited, Kingsthorpe, Northampton, England, both British companies Application May 10, 1951, Serial No. 225,478 In Great Britain January 25, 1950 17 Claims. 1

'I'h1s invention relates to improvements in and relating to electrical resistors and resistance elements therefor and is more particularly concerned with the provision of an improved resistance element and a resistor incorporating such an element, suitable for use inthe electronic art.

For many purposes, resistors having a resistance value of from 0.1- megohms are common- 1y required, but for particular applications it may be necessary to employ resistors having values of several hundred megohms. The expression high resistance value or high value as employed herein, is intended to embrace resistance values ranging from one-tenth of a megohm to several hundred megohms. H

Various types of resistors for use in radio and similar equipment are at present marketed, but all of them suffer from certain inherent disadvantages, which detract from their efficient use in modern electronic apparatus. There is a constant demand from the electrical industry for a resistor, which shall have a high resistance value and a stable resistance, shall be substantially noise free and have a low, preferably positive, temperature coefiicient of resistance and which shall at the same time be compact and readily handlable. So far as We are aware, there is no resistor at present available which fully meets these requirements.

The principal object of this invention is to provide an improved resistance element, by means of which resistors may be prepared which exhibit in use an improved performance and which more adequately comply with the requirements of the electrical industry than do existing types of resistors.

Another object of the invention is to provide an improved resistance element by means of which a resistor having the characteristics of high value, improved stability and substantial freedom from noise can be prepared.

Another object is to provide a metal film resistor which is compact, and, at the same time, exhibits the characteristics of stability combined with a low temperature coefiicient of resistance.

A further object is to provide a resistance element by means of which a high value resistor may be obtained without resort to helical groov- The manner in which the above and other objects are attained will be readily understood from the following detailed description, taken in con- Junction with the lacc mpanyingy drawings,

which are given merely by way of example and are not to be regarded as in any way limitative, the scope of the invention being defined by the appended claims.

In the drawings, Figure 1 shows a partly completed high value resistor embodying the features of our invention, Figure 2 shows the completed resistor and Figure 3 shows one method of forming the metallised filament or fibre constituting the resistance element.

During the course of extensive research carried out by us in an endeavour to meet the above I requirements, experiments were conducted with resistance elements composed of metallic films applied to suitable insulating bases and it was found that, whilst a thin metallic film would enable a high resistance value to be obtained, the resistance was not stable, whereas a relatively thick metallic film, whilst providing the required degree of stability, would not enable a high value resistor to be obtained unless the element were of such a length as to be impracticable for electronic purposes.

The problem that confronted us, therefore was to provide a resistance element, the current con ducting path of which would besufiiciently thick to produce a stable resistance and at the same time could be made of sumcient length to give a high value in a finished resistor, without the latter being unduly bulky or elongated As the result of our investigations, we have found that a satisfactory resistance element can be obtained by coating a filament, strand or fibre of non-conducting material with a relatively thick film composed of a selected metal or metals, the filament, strand or fibre being of such a nature that the metal coating can be fired thereon and preferably having sufiicient flexibility and strength as to render it capable of being wound on a small diameter former, such as a A" diameter former commonly used for miniature resistors. By this means a compact resistor of readily handlable size having a stable resistance and a high value can be obtained.

Our invention, therefore, broadly comprises, as an article of manufacture, an electric resistance clement comprising'a fiament, strand or fibre of non-conductive heat-resisting inorganic material having on the outer surface thereof a firmly adherent relatively thick fired-on film or layer consisting wholly or predominantly of a metal or alloy selected from the group consisting of gold, platinum and goldzplatinum alloys.

By heat-resisting material as used herein and in the claims is meant a material capable of withstanding a firing temperature of at least .00 C. and by relatively thick film or layer" is meant a film or layer haivng a resistance of between and 1000 ohms/sq.

The material of which the filament, strand or fibre is formed may advantageously be glass or a glass-like material and of these materials we prefer to use glass.

If the conducting film or layer is formed of a gold platinum alloy, we have found that an 80:20 goldzplatinum alloy will give excellent results. A resistor formed with this alloy will exhibit a high resistivity and a low temperature coefficient of resistance.

Other metals, in addition to gold and/or platinum, may, if desired, be included in the conducting film or layer.

According to a further feature of the invention, we provide a method for the manufacture of an electrical resistance element which comprises the steps of applying to the surface of a filament, strand or fibre of non-conductive heatresisting inorganic material a coating of a solution containing a compound of gold or platinum, or a mixture of gold and platinum compounds dissolved therein and subsequently heating the coated filament, strand or fibre to decompose the compound or compounds and cause the resulting metal or alloy film to adhere firmly thereto.

A resistance element embodying the novel features of our invention may be made by applying to the surface of a filament, strand or fibre of non-conductive heat-resisting inorganic material and preferably having an inherent flexibility and strength such as to enable it to be wound on a former, a coating of a solution containing a compound of gold or platinum or a mixture of gold and platinum compounds dissolved therein and subsequently heatin' the coated filament, strand or fibre to decompose the compound or compounds and cause the resulting metal or alloy film to adhere firmly thereto.

The solution may, for example, comprise a mixture of a gold and/ or a platinum compound and. a cellulose derivative dissolved in a suitable solvent or solvent mixture to which is preferably added an adhesion promoting agent or flux. W e have found a solution of platinic chloride, bismuth chloride and nitro-cellulose in a solvent mixture comprising acetone and alcohol, which, on firing, will produce a platinum film, to be satisfactory for our purpose.

A temperature coefiicient lower than that given by a film of platinum alone may, however, be obtained by the use of a solution consisting of the sulphoresinates of gold and platinum (in the proportion of 4 parts of gold to one part of platinum) and bismuth resinate in an essential oil solvent mixture.

The filament, strand or fibre may advantageously be coated by passing it through a bath containing the desired coating solution or over, and in contact with, a pad moistened with the said solution.

The following are examples of solutions which may be employed to form a resistance element in accordance with the invention by coating a glass fibre therewith and then heating to burn away the organic matter and leave an adherent gold or platinum or gold platinum alloy film on the fibre. It is to be understood, however, that the invention is, in no way, limited to these examples.

4 Example I Percen Platinic chloride 5 Alcohol 8 Nitro-cellulose 8 Acetone This solution, when fired, will produce a film or layer of platinum.

Example H Percent Gold (as sulpho-resinate) 7.0 Rhodium (as sulpho-reslnate) W 0.1 Bismuth (as resinate) 0.2 Oil of turpentine 43.0 Oil of lavender 10.0

Nitro-benzol 10.0 Colophony 21.7

This solution, when fired, will produce a film or layer of gold.

Example 111 Perce .t Gold (as sulpho-resinate) 5.6 Platinum (as sulpho-resinate) 1.4 Rhodium 0.1 Bismuth (as resinate) 0.2 Oil of turpentine 43.0 Oil of lavender 1..0 Nitro-benzol 10.0 Colophony 21.7

This solution, when fired, will produce a film or layer consisting of a gold-platinum alloy.

If desired, a further coating or further coatings of the solution may be applied depending on the required final thickness and resistance of the metallising film or layer.

In forming a high value resistor with the of our improved resistance element, the latter is wound on an insulating former, which is preferably of circular cross-section, although other cross-sections may be employed. In this marine. owing to the extreme attenuation of the conducting path, a high value resistor of readily hand-- lable size may be obtained.

The method may, advantageously, be carried out as a continuous process comprising drawing or feeding a continuous length of filament or fibre through a gold, platinum or gold and platinum metallising solution, passing the coated fibre through a furnace to cause the organic matter in the coating to burn away and leave a firmly adherent film or layer of metal or alloy on the fibre and then winding the metallised fibre on to a reel or drum.

To complete a resistor embodying our proved resistance element, the required length of metallised filament or fibre is wound from th drum on to an insulating former, e. g. of suitable ceramic material, and external connections are made to the element in any suitable manner.

Referring now to Figure 1 of the drawings, the resistor consists of a former i of ceramic material on which is wound a resistance element in the form of a glass fibre 2, which has been previously metallised in accordance with this invention. On each end of the former i is a 3 to which the free ends l of the metallised fibre 2 are attached, for example by soldering. as shown at 5. 6 are the usual lead wires which are soldered to the outer ends of the caps 3 at for connecting the resistor in an electro c circuit.

The completed resistor is covered with a lo er of a silicone resin varnish 8 (Figure 2) or other megohm may be constituted as follows:

Fibre (glass) 0.001 in. dia. Resistance of film 100 ohms/square.

Resistance of 1 inch of 31800 ohms.

metallised fibre.

Length required for 1 31.4 inches.

megohm.

Former 0.160 in. dia.

Number of turns -1 63.

Pitch of turns 0.004 in.

Length of winding /4 in.

Another resistor embodying the invention and having a resistance value of 10 megohms may be constituted as follows:

Fibre (glass) 0.001 dia. Resistance of film 300 ohms/square. Resistance of 1 inch of metal- 95400 ohms.

lised fibre. Length of fibre required for 10 104.6".

megohms. Former A dia. Number of turns 133. Pitch of turns 0.004". Length of winding 0.53".

Figure 3 illustrates diagrammatically the preferred manner of making a resistance element embodying the features of the invention.

Referring now to this Figure 3, 9 represents a reel or drum upon which is wound a length of glass fibre 10. The fibre I is drawn from the drum 9 and passes between a pair of superposed felt pads II and !2, supported in a vessel or bath [3 containing the desired metallising solution 14, the pad II being partly immersed in the said solution.

The glass fibre l0, when it emerges from the vessel 13, is thus covered with a thin coating of the metallising solution Hi. The coated fibre 10 now passes into a muflie furnace containing an electric resistance heating element l6, where the coated fibre is first heated to a temperature Within a range of 450-550" C., the particular temperature depending on the particular composition of the glass constituting the fibre, to burn awai the organic matter contained in the coating solution and cause the metal in the solution to adhere firmly thereto and is then annealed, after which the now metallised and annealed fibre l0 passes out of the furnace and is wound on to a drum l'l.

It is to be understood that whilst, in the above. one embodiment of the invention and the manner in which it is to be performed has been described, modification maybe made to the details thereof, without departing from the spirit of the invention.

What we claim is:

1. A method of making an electrical resistance element which comprises the steps of applying to a glass filament a solution of the sulphoresinate of at least one metal selected from the group consisting of gold and platinum dissolved in an essential oil solvent mixture, firing said coated filament at a temperature sufficient to burn away the organic matter and cause an adherent metallic film to adhere to'said filament, and then winding a continuous length of said filament around the outer periphery of an insulating former, and in which the solution has the following composition, namely:

Percent Gold (as su1ph0-resinate) 5.6 Platinum (as sulpho-resinate) 1.4 Rhodium 0.1 Bismuth (as resinate) 0.2 Oil of turpentine 43.0 Oil of lavender 18.0 Nitro-benzol 10.0 Colophony 21.7

2. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of filament of a material selected from the group consisting of glass and glass-like materials having on the outer surface thereof a firmly adherent relatively thick substantiall uniform film of a gold platinum alloy wound around the outer periphery of said former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path. 7

3. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of glass filament having on the outer surface thereof a firmly adherent relatively thick substantially uniform film consisting of a goldzplatinum alloy wound around the outer periphery of said former for a plurality of turns in close proximity to each other.

4. A method of making an electrical resistance element which comprises the steps of applying to the outer surface of a continuous filament of glass a substantially uniform layer consisting of gold-platinum alloy and then winding a continuous length of said coated filament around the outer periphery of a cylindrical insulating former for a plurality of turns in close proximity to each other thereby providing an attenuated current path.

5. A method of making an electrical resistance element which comprises the steps of drawing a glass filament through a bath containing a solution consisting of platinic chloride, bismuth chloride and nitrocellulose dissolved in alcohol and acetone to form a coating of said solution on said filament; heating said coated filament to burn away the organic matter in said coating and cause a film of platinum to adhere firmly to said filament; and then winding a continuous length of said filament around the outer periphery of an insulating former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

6. A method according to claim 5 in which the solution has the following composition, namely Percent Platinic chloride 8 Alcohol 8 Nitro-cellulose 8 Acetone 1 76 7. A method of making an electrical resistance element which comprises the steps of applying to a continuous filament of glass a solution of the sulphoresinate of metal selected from the group consisting of gold, platinum, and goldplatinum alloys dissolved in an essential oil solvent mixture; firing said coated filament at a temperature sufiicient to burn away the organic matter and cause anadherent metallic film to adhere to said filament; and then winding a continuous length of said filament around the outer periphery of an insulating former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

8. A method according to claim 7 in which the solution has the following composition, namely Percent Gold (as sulpho-resinate) 7.0 Rhodium (as sulpho-resinate) 0.1 Bismuth (as resinate) 0.2 Oil of turpentine 43.0 Oil of lavender 18.0 Nitro-benzol 10.0 Colophony 21.7

9. An electrical resistance element comprising an insulating former carrying a conductive element comprising a continuous length of filament of a material selected from the group consisting of glass and glass-like materials having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film consisting of metal selected from the group consisting of gold, platinum, and gold-platinum alloys wound around the outer periphery of said former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

10. An electrical resistance element comprising an insulating former carrying a conductive element comprising a continuous length of filament of a material selected from the group consisting of glass and glass-like materials having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film of gold Wound around the outer periphery of said former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

11. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of filament of a material selected from the group consisting of glass and glass-like materials having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film of platinum wound around the outer periphery of said former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

12. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of glass filament having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film consisting of metal selected from the group consisting of gold, platinum, and gold-platinum alloys wound around the outer periphery of said former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

13. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of glass filament having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film consisting of gold wound around the outer periphery of said former for a plurality of turns in close proximity to each other.

14. An electrical resistance element comprising an insulating former carrying a conductive element comprising a single continuous length of glass filament having on the outer surface thereof a firmly adherent, relatively thick, substantially uniform film consisting of platinum wound around the outer periphery of said former for a plurality of turns in close proximity to each other.

15. A method of making an electrical resistance element which comprises the steps of applying to the outer surface of a continuous filament of a material selected from the group consisting of glass and glass-like materials a substantially uniform layer consisting of metal selected from the group, consisting of gold, platinum, and goldplatinum alloys, and then winding a continuous length of said coated filament around the outer periphery of an insulating former for a plurality of turns in close proximity to each other, thereby providing an attenuated current path.

16. A method of making an electrical resistance a element which comprises the steps of applying to the outer surface of a continuous filament of a material selected from the group consisting of glass and glass-like materials a solution containing a compound of metal selected from the group consisting of gold, platinum, and gold-platinum alloys dissolved therein; heating said coated filament to decompose at least said compound and cause a metallic film to adhere to said filament; and then winding a continuous length of said coated filament around the outer periphery of an insulating former for a plurality of trans in close proximity to each other, thereby providing an attenuated current path.

17. A method of making an electrical resistance element which comprises the steps of winding around the outer periphery of a cylindrical insulating former for a plurality of turns in close proximity to each other, a continuous length of a filament of a material selected from the group consisting of glass and glass-like materials having on its outer surface a firmly adherent, relatively thick, substantially uniform film consisting of metal selected from the group consisting of gold, platinum, and gold-platinum alloys, thereby providing an attenuated current path, and providing a stable resistance having a predetermined high constant value.

FRANK ENOCH KERRIDGE.

MICHAEL BELHAM.

GRAHAM PEARCE.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. A METHOD OF MAKING AN ELECTRICAL RESISTANCE ELEMENT WHICH COMPRISES THE STEPS OF APPLYING TO A GLASS FILAMENT A SOLUTION OF THE SULPHORESINATE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF GOLD AND PLATINUM DISSOLVED IN AN ESSENTIAL OIL SOLVENT MIXTUE, FIRING SAID COATED FILAMENT AT A TEMPERATURE SUFFICIENT TO BURN AWAY 